The Airbnb team open-source its Swift code specification

protocol SpaceThing {
  // ...
}

class Spacefleet: SpaceThing {

  enum Formation {
    // ...
  }

  class Spaceship {
    // ...
  }

  var ships: [Spaceship] = []
  static let worldName: String = "Earth"

  func addShip(_ ship: Spaceship) {
    // ...
  }
}

let myFleet = Spacefleet()Copy the code

// WRONG
let rightTitleMargin: CGFloat
let leftTitleMargin: CGFloat
let bodyRightMargin: CGFloat
let bodyLeftMargin: CGFloat

// RIGHT
let titleMarginRight: CGFloat
let titleMarginLeft: CGFloat
let bodyMarginRight: CGFloat
let bodyMarginLeft: CGFloatCopy the code

// WRONG
let title: String
let cancel: UIButton

// RIGHT
let titleText: String
let cancelButton: UIButtonCopy the code

// WRONG
class AIRAccount {
  // ...
}

// RIGHT
class Account {
  // ...
}Copy the code

// WRONG
let host: Host = Host()

// RIGHT
let host = Host()Copy the code

enum Direction {
  case left
  case right
}

func someDirection() -> Direction {
  // WRONG
  return Direction.left

  // RIGHT
  return .left
}Copy the code

final class Listing { init(capacity: Int, allowsPets: Bool) { // WRONG self.capacity = capacity self.isFamilyFriendly = ! allowsPets // `self.` not required here // RIGHT self.capacity = capacity isFamilyFriendly = ! allowsPets } private let isFamilyFriendly: Bool private var capacity: Int private func increaseCapacity(by amount: Int) { // WRONG self.capacity += amount // RIGHT capacity += amount // WRONG self.save() // RIGHT save() } }Copy the code

// WRONG
let rowContent = [
  listingUrgencyDatesRowContent(),
  listingUrgencyBookedRowContent(),
  listingUrgencyBookedShortRowContent()
]

// RIGHT
let rowContent = [
  listingUrgencyDatesRowContent(),
  listingUrgencyBookedRowContent(),
  listingUrgencyBookedShortRowContent(),
]Copy the code

// WRONG
func whatever() -> (Int, Int) {
  return (4, 4)
}
let thing = whatever()
print(thing.0)

// RIGHT
func whatever() -> (x: Int, y: Int) {
  return (x: 4, y: 4)
}

// THIS IS ALSO OKAY
func whatever2() -> (x: Int, y: Int) {
  let x = 4
  let y = 4
  return (x, y)
}

let coord = whatever()
coord.x
coord.yCopy the code

// WRONG
let rect = CGRectMake(10, 10, 10, 10)

// RIGHT
let rect = CGRect(x: 0, y: 0, width: 10, height: 10)Copy the code

// WRONG
var rect = CGRectZero
var width = CGRectGetWidth(rect)

// RIGHT
var rect = CGRect.zero
var width = rect.widthCopy the code

// WRONG
var something : Double = 0

// RIGHT
var something: Double = 0Copy the code

// WRONG
class MyClass : SuperClass {
  // ...
}

// RIGHT
class MyClass: SuperClass {
  // ...
}Copy the code

// WRONG
var dict = [KeyType:ValueType]()
var dict = [KeyType : ValueType]()

// RIGHT
var dict = [KeyType: ValueType]()Copy the code

// WRONG
func doSomething()->String {
  // ...
}

// RIGHT
func doSomething() -> String {
  // ...
}Copy the code

// WRONG
func doSomething(completion: ()->Void) {
  // ...
}

// RIGHT
func doSomething(completion: () -> Void) {
  // ...
}Copy the code

// WRONG
if (userCount > 0) { ... }
switch (someValue) { ... }
let evens = userCounts.filter { (number) in number % 2 == 0 }
let squares = userCounts.map() { $0 * $0 }

// RIGHT
if userCount > 0 { ... }
switch someValue { ... }
let evens = userCounts.filter { number in number % 2 == 0 }
let squares = userCounts.map { $0 * $0 }Copy the code

// WRONG
if case .done(_) = result { ... }

switch animal {
case .dog(_, _, _):
  ...
}

// RIGHT
if case .done = result { ... }

switch animal {
case .dog:
  ...
}Copy the code

// WRONG
func doSomething() -> Void {
  ...
}

// RIGHT
func doSomething() {
  ...
}Copy the code

// WRONG
func method(completion: () -> ()) {
  ...
}

// RIGHT
func method(completion: () -> Void) {
  ...
}Copy the code

// WRONG

match(pattern: pattern)
  .compactMap { range in
    return Command(string: contents, range: range)
}
  .compactMap { command in
    return command.expand()
}

values.forEach { value in
  print(value)
  }

// RIGHT

match(pattern: pattern)
  .compactMap { range in
    return Command(string: contents, range: range)
  }
  .compactMap { command in
    return command.expand()
  }

values.forEach { value in
  print(value)
}Copy the code

// WRONG let evenSquares = numbers.filter {$0 % 2 == 0}.map { $0 * $0 } // RIGHT let evenSquares = numbers.filter { $0 %  2 == 0 }.map { $0 * $0 }Copy the code

// WRONG let capacity = 1+2 let capacity = currentCapacity ?? 0 let mask = (UIAccessibilityTraitButton|UIAccessibilityTraitSelected) let capacity=newCapacity let latitude = Region. The center. The latitude - region. Span. LatitudeDelta / 2.0 / / RIGHT capacity = 1 + 2 let capacity = currentCapacity?? 0 let mask = (UIAccessibilityTraitButton | UIAccessibilityTraitSelected) let capacity = newCapacity let latitude = Region. The center. The latitude - (region) span) latitudeDelta / 2.0)Copy the code

// WRONG
class MyClass: NSObject {

  init() {
    super.init()
    someValue = 5
  }

  var someValue: Int!
}

// RIGHT
class MyClass: NSObject {

  init() {
    someValue = 0
    super.init()
  }

  var someValue: Int
}Copy the code

// WRONG class TextField { var text: String? { didSet { guard oldValue ! = text else { return } // Do a bunch of text-related side-effects. } } } // RIGHT class TextField { var text: String? { didSet { updateText(from: oldValue) } } private func updateText(from oldValue: String?) { guard oldValue ! = text else { return } // Do a bunch of text-related side-effects. } }Copy the code

//WRONG
class MyClass {

  func request(completion: () -> Void) {
    API.request() { [weak self] response in
      if let strongSelf = self {
        // Processing and side effects
      }
      completion()
    }
  }
}

// RIGHT
class MyClass {

  func request(completion: () -> Void) {
    API.request() { [weak self] response in
      guard let strongSelf = self else { return }
      strongSelf.doSomething(strongSelf.property)
      completion()
    }
  }

  func doSomething(nonOptionalParameter: SomeClass) {
    // Processing and side effects
  }
}Copy the code

// WRONG func age(of person, bornAt timeInterval) -> Int { // ... } func jump(person: Person) { // ... } // RIGHT class Person { var bornAt: TimeInterval var age: Int { // ... } func jump() { // ... }}Copy the code

private let privateValue = "secret"

public class MyClass {

  public static let publicValue = "something"

  func doSomething() {
    print(privateValue)
    print(MyClass.publicValue)
  }
}Copy the code

func didSubmitText(_ text: String) {
  // It's unclear how this was called with an empty string; our custom text field shouldn't allow this.
  // This assert is useful for debugging but it's OK if we simply ignore this scenario in production.
  guard text.isEmpty else {
    assertionFailure("Unexpected empty string")
    return
  }
  // ...
}

func transformedItem(atIndex index: Int, from items: [Item]) -> Item {
  precondition(index >= 0 && index < items.count)
  // It's impossible to continue executing if the precondition has failed.
  // ...
}

func makeImage(name: String) -> UIImage {
  guard let image = UIImage(named: name, in: nil, compatibleWith: nil) else {
    fatalError("Image named \(name) couldn't be loaded.")
    // We want the error message so we know the name of the missing image.
  }
  return image
}Copy the code

class PriceBreakdownViewController { private let acceptButton = UIButton() private func setUpAcceptButton() { acceptButton.addTarget( self, action: #selector(didTapAcceptButton), forControlEvents: .TouchUpInside) } @objc private func didTapAcceptButton() { // ... }}Copy the code